Re: [Lsr] How to forward the solutions for "Prefixes Unreachable Notification" problem

[Robert Raszuk <[e-mail]>]

Hi Les,

Yes you are correct. It is a classic pull vs push model.

Push gives you notification about state. That's it.

Pull gives you much more as it includes e2e elements of the data plane - of
course for a bit higher cost.

I would not disregard any of the above.

We have been having similar discussions in the past - I am sure some of us
still remember MARP proposal from Alvaro and Russ inspired by David Oran's
idea. While it was L2 switch centric I mention it here to highlight how a
cool idea went nowhere ... ref:
https://tools.ietf.org/id/draft-retana-marp-02.txt and how the end to end
pull model overwhelmed it.

At least we could learn from it for the WAN now. Perhaps fully
coincidentally it is also very similar to proposed by Tony pub-sub model.

Thx,
R.

On Thu, Jan 27, 2022 at 1:49 AM Les Ginsberg (ginsberg) <ginsberg=
[e-mail]> wrote:

> Chris -
>
> The scale request comes from real customers. So, it is understandable for
> you to be "aghast" - but it is a real request.
>
> As far as BFD goes, my opinion is this won’t scale. There is a significant
> difference between operating sessions which continuously monitor liveness
> in a full mesh versus using some approach which only triggers network-wide
> traffic when some topology change is locally detected. There are multiple
> approaches being discussed which do the latter - but BFD is not one of them.
>
> You can disagree - or - as Greg has done - say we don’t really have to
> consider this scale. I am not going to try to convince you otherwise.
> But if so you aren’t solving the problem we have been asked to solve.
>
>    Les
>
>
> > -----Original Message-----
> > From: Christian Hopps <[e-mail]>
> > Sent: Wednesday, January 26, 2022 2:15 PM
> > To: Les Ginsberg (ginsberg) <[e-mail]>
> > Cc: Greg Mirsky <[e-mail]>; Aijun Wang
> > <[e-mail]>; [e-mail]
> > Subject: Re: [Lsr] How to forward the solutions for "Prefixes Unreachable
> > Notification" problem
> >
> >
> > "Les Ginsberg (ginsberg)" <ginsberg=[e-mail]> writes:
> >
> > > Greg –
> > >
> > > With 100K PE scale, we are talking about 100K BFD sessions/PE and
> > > close to 5 million BFD sessions network-wide.
> > >
> > > Eliminating one of the options we are discussing is admittedly a
> > > small step, but still worthwhile.
> >
> > Hang on a sec. :)
> >
> > We are starting off with this GINORMOUS network with 100,000 PE routers!
> > Why would 5 million sessions of anything over this gigantic network of
> > routers be a reason to disregard it as a solution? (How many total
> routers are
> > there BTW?)
> >
> > If you build something gignatic *everything* is going to scale way up.
> To use
> > an oldie but a goodie: TANSTAAFL.
> >
> > Thanks,
> > Chris.
> >
> >
> > >
> > >
> > > However, If you still want to continue to advocate for BFD, I will
> > > say no more.
> > >
> > >
> > >
> > >    Les
> > >
> > >
> > >
> > > From: Lsr <[e-mail]> On Behalf Of Greg Mirsky
> > > Sent: Tuesday, January 25, 2022 7:06 PM
> > > To: Aijun Wang <[e-mail]>
> > > Cc: lsr <[e-mail]>
> > > Subject: Re: [Lsr] How to forward the solutions for "Prefixes
> > > Unreachable Notification" problem
> > >
> > >
> > >
> > > Hi Aijun,
> > >
> > > I believe that under Option D you can add multihop BFD per RFC 5883.
> > > No new protols needed.
> > >
> > >
> > >
> > > Regards,
> > >
> > > Greg
> > >
> > >
> > >
> > > On Tue, Jan 25, 2022, 18:17 Aijun Wang <[e-mail]>
> > > wrote:
> > >
> > >     Hi, All:
> > >
> > >
> > >
> > >     As Peter’s example and Acee’s suggestions, let’s focus on the
> > >     following problem to think how to solve it efficiently and
> > >     reasonably:
> > >
> > >     Scenario: 100 areas each with 1000 PEs (100K total PEs) with 2
> > >     ABRs per area
> > >
> > >     Problem: Overlay services(BGP or Tunnel) that rely on the IGP
> > >     needs to be notified immediately when the remote Peer failed, to
> > >     assist such overlay service accomplish fast switchover(how to
> > >     switchover is out of the discussion)
> > >
> > >     Potential Solutions:
> > >
> > >        There are now mainly four categories of the solutions, as
> > >     described below and their brief analysis:
> > >
> > >        Category A: PUA/PULSE. Utilizes the existing IGP mechanism to
> > >     transport/flooding the notification message.
> > >
> > >        Category B: Detail/Important Prefixes Leaks. Bypass the
> > >     summary side-effect for some detailed/important prefixes by
> > >     leaking/not summarize them into each area.
> > >
> > >        Category C: BGP based solution: Utilize the existing BGP
> > >     infrastructure to transport the notification message
> > >
> > >        Category D: OOB Solution. Design some new OOB protocol to
> > >     transport the notification message.
> > >
> > >
> > >
> > >     Because we are in LSR WG, and people are all IGP experts. After
> > >     the intense discussion, can we now focus on the Category A/B?
> > >
> > >     It is very curious that LSR WG will and should produce some BGP
> > >     or OOB based solution. I think they may be feasible, but should
> > >     be evaluated/discussed by other WGs.
> > >
> > >     Or else, I think we can’t converge to one standard solution.
> > >
> > >
> > >
> > >     >From the POV of the operator, we prefer to the IGP based
> > >     solution. If there is no unsolvable concerns, let’s accept it. I
> > >     think there is enough interests and experts to accomplish this
> > >     task.
> > >
> > >
> > >
> > >     Best Regards
> > >
> > >
> > >
> > >     Aijun Wang
> > >
> > >     China Telecom
> > >
> > >
> > >
> > >     _______________________________________________
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> > >
> > >
> > >
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